Field of the Invention
This invention relates to polyurethane prepolymer containing adhesives that are liquid at room temperature and that do not phase separate under typical storage and use conditions and that can be cured by exposure to moisture or active hydrogen-containing curing agents. The polyurethane prepolymer adhesives exhibit surprisingly good adhesion to plastics such as fiberglass reinforced plastics (“FRP”).
Brief Description of Related Technology
Liquid moisture curable polyurethane adhesives are known. Indeed, Henkel Corporation presently sells and offers for sale liquid moisture curable polyurethane adhesive products under the tradenames Macroplast® UR and Macroplast® SIA, each of which has been met with considerable market success.
Liquid moisture curable polyurethane adhesive can be modified by some additives. For example, plasticizer oils have been used in the past to improve the rheology of such polyurethane adhesive. Adhesion promoters have also been used in the past to improve the adhesion to substrates of such polyurethane adhesive. However, in some instances, use of the plasticizer oil leads to phase separation, which is undesirable.
In the context of hot melt adhesives, which change phase depending on the temperature to which they are exposured, moisture curable polyurethane based materials are known. For instance, Henkel Corporation has been responsible for advances in such technology as defined and claimed for instance in U.S. Pat. Nos. 6,136,136 (Heidler), 6,221,978 (Li), and 6,635,722 (Li).
U.S. Pat. No. 5,786,085 (Tzeng) is directed to and claims a ridge cap formed from an asphaltic foam material comprising (1) a layer of said asphaltic foam material having an upper surface and a lower surface; (2) a layer of granules embedded in said upper surface of said layer of asphaltic foam material, said granules forming a decorative and/or protective layer of said ridge cap; and (3) an elastomeric strip connected to said layer of asphaltic foam material along a central axis of said layer and covered with said granules, where said ridge cap is bendable along said central axis. In the '085 patent, the asphaltic foam is a polyurethane material, and additives such as plasticizers and viscosity reducers are noted as possible reactants
U.S. Pat. No. 5,932,646 (Roberts) is directed to and claims a composition of matter for waterproofing a surface of a wall comprising from about 30 to about 55 parts by weight of a polymeric base, the polymer base including from about 20 to about 45 parts by weight of a hydrocarbon resin, and from about 55 to about 80 parts by weight of an elastomeric copolymer having units selected from styrene, isoprene, butadiene, ethylene, butylene and mixtures thereof where the hydrocarbon resin and the elastomeric copolymer total about 100 parts by weight; and from about 45 to about 70 parts by weight of a solvent system, where the solvent system includes a blend of petroleum distillates and heptane, where the heptane comprises n-heptane, and where the polymer base and the solvent system total about 100 parts by weight.
Although liquid moisture curable polyurethane adhesives have been in industrial usage for several decades, there stands room for improvement. For example, adhesion to plastics such as FRP can be sometimes difficult. Production of such an adhesive also requires high processing temperature, which translates into higher than desired energy costs. The stability of such an adhesive can also stand improvement. It would be desirable to have liquid moisture curable polyurethane adhesives, which can be produced at lower processing temperatures, have improved stability, and have improved adhesion to plastics such as FRP.